Revert "channeldb: remove unsupported migrations"

This reverts commit 3ab4c749c6.

channeldb/legacy_serialization.go

@@ -0,0 +1,55 @@
+package channeldb
+
+import (
+	"io"
+)
+
+// deserializeCloseChannelSummaryV6 reads the v6 database format for
+// ChannelCloseSummary.
+//
+// NOTE: deprecated, only for migration.
+func deserializeCloseChannelSummaryV6(r io.Reader) (*ChannelCloseSummary, error) {
+	c := &ChannelCloseSummary{}
+
+	err := ReadElements(r,
+		&c.ChanPoint, &c.ShortChanID, &c.ChainHash, &c.ClosingTXID,
+		&c.CloseHeight, &c.RemotePub, &c.Capacity, &c.SettledBalance,
+		&c.TimeLockedBalance, &c.CloseType, &c.IsPending,
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	// We'll now check to see if the channel close summary was encoded with
+	// any of the additional optional fields.
+	err = ReadElements(r, &c.RemoteCurrentRevocation)
+	switch {
+	case err == io.EOF:
+		return c, nil
+
+	// If we got a non-eof error, then we know there's an actually issue.
+	// Otherwise, it may have been the case that this summary didn't have
+	// the set of optional fields.
+	case err != nil:
+		return nil, err
+	}
+
+	if err := readChanConfig(r, &c.LocalChanConfig); err != nil {
+		return nil, err
+	}
+
+	// Finally, we'll attempt to read the next unrevoked commitment point
+	// for the remote party. If we closed the channel before receiving a
+	// funding locked message, then this can be nil. As a result, we'll use
+	// the same technique to read the field, only if there's still data
+	// left in the buffer.
+	err = ReadElements(r, &c.RemoteNextRevocation)
+	if err != nil && err != io.EOF {
+		// If we got a non-eof error, then we know there's an actually
+		// issue. Otherwise, it may have been the case that this
+		// summary didn't have the set of optional fields.
+		return nil, err
+	}
+
+	return c, nil
+}